The invention relates generally to the field of threaded fasteners, and more specifically, to a spring washer that is adapted to be non-removably retained on such a fastener.
Threaded fasteners, such as screws, bolts and the like, are commonly used in industry, particularly where it is desired to provide a strong, sturdy connection between two workpieces that is not intended to be permanent. Such fasteners may be used with threaded nuts, or may simply thread through holes provided in one or both of the workpieces to be joined. The fasteners are available in various standard sizes and designs which include differently sized and oriented threads, differently shaped heads, and different shank lengths. The variety of sizes and designs permit the selection of the optimum fastener for each particular application.
It is common practice when using threaded fasteners to provide a spring washer between the head of the fastener and the workpiece. Many spring washers serve a dual purpose. Firstly, as in the case of conventional flat washers, the spring washers typically provide an enlarged surface against which the head of the fastener can turn to help prevent scratching or other damage to the workpiece during tightening of the fastener, and after tightening, to help prevent the head of the fastener from being pulled through the workpiece under excessive load. Secondly, the spring washers resiliently bias the head of the fastener away from the workpiece, causing the threads of the fastener to grip the workpiece more tightly thereby to prevent loosening of the fastener due to workpiece vibration and the like.
Ordinarily, the washers and fasteners are provided separately to a worker who uses them, and the worker must place the washer on the fastener in advance of their use. The operation of placing a washer on the threaded end of the fastener, while a simple one, can become a considerable time limiting factor in an assembly-line manufacturing operation, such as that employed in the manufacture of automobiles and other vehicles, where many such fasteners are typically installed and where the time the product spends at each assembly line station is necessarily limited. Also, if there are no means for retaining the washer on the fastener after it is inserted, the washer can, and often does, fall off as the worker manipulates the fastener into position for engaging the workpiece. This leads to further delays, as it requires repositioning of the washer. Thus, it is desirable to provide a spring washer that, once positioned on a threaded fastener, remains securely in place thereon during manipulation of the fastener.
Attempts have been made heretofore to provide threaded fasteners having washers already fitted thereon. These attempts, however, have required that the fastener itself be specially designed to retain the washer, or alternatively, have required that fastener manufacturing process be modified so that the threads of the fastener are rolled after the washer is placed on the blank fastener shank. Both of these alternatives undesirably add to the expense of the fastener.